1. Field of the Invention
The present invention relates to a fully enclosed type motor with outer fans, which is applicable to a car-driving motor, etc.
2. Description of the Related Art
In general, in a railway car, a car-driving motor is mounted on a bogie disposed under the car body. A torque of the motor is transmitted to wheels via a gear unit, thus driving the car. This type of conventional motor has a structure shown in FIG. 1.
In FIG. 1, the conventional car-driving motor has a cylindrical frame 1 that is a fixed-side member. A bracket 2 is attached to one end of the frame 1, and a housing 3 is attached to a central part of the other end of the frame 1. Both end portions of a rotor shaft 6 are rotatably supported on bearings 4 and 5 provided at central parts of the bracket 2 and housing 3.
A rotor core 7 is fixed to an axially middle part of the rotor shaft 6. Rotor bars 8 are embedded in a number of grooves formed in the outer peripheral surface of the rotor core 7. Both end portions of each rotor bar 8 are protruded from the rotor core 7. The protruded parts of the rotor bars 8 are integrally coupled by end rings 201. Thus, a cage rotor of an induction motor is constituted. A plurality of vent holes 7a are formed in the rotor core 7 so as to axially penetrate the rotor core 7, and both end portions of the rotor core 7 are sandwiched by core holders 202 having vent holes.
A cylindrical stator core 10 is attached to an inner peripheral part of the frame 1. A stator coil 11 is provided in a number of grooves formed in the inner peripheral surface of the stator core 10. Coil end portions of the stator coil 11 are protruded from both sides of the stator core 10.
A uniform gap 200 is defined between the inner peripheral surface of the stator core 10 and the outer peripheral surface of the rotor core 7. A drive-side end 6a of the rotor shaft 6 is projected from the motor body. A coupler for coupling with a drive gear unit is attached to the projected drive-side end 6a. 
A ventilation fan 9 is fixed to that part of the rotor shaft 6, which is located within the motor body. The ventilation fan 9 has a plurality of blades 9a extending radially from the center of the fan 9. A plurality of exhaust ports 1a are formed in the circumferential direction of the frame 1 in that part of the frame 1, which is opposed to an outer peripheral part of the ventilation fan 9.
An air inlet 1b is provided at an upper part of the non-driving-side part of the frame 1. An air filter unit 12 is provided so as to cover the air inlet 1b. A filter 12a for capturing dust is attached to the entire area of an outside air intake port of the filter unit 12.
The entirety of the motor shown in FIG. 1 is secured to the bogie such that attachment arms provided on the frame 1 are fastened to the bogie by means of bolts. A torque of the motor is transmitted to the gear unit via the coupler attached to the end portion 6a of the rotor shaft 6, and then to the wheels, thereby driving the car.
In operation of the motor, the stator coil 11 and rotor bars 8 of the motor generate heat. A rise in temperature of the motor is suppressed by feeding outside air into the motor and cooling the stator coil 11 and rotor bars 8. The cooling operation is described below.
When the motor is operated, the ventilation fan 9 is rotated by the rotor shaft 6 and air within the motor is exhausted from the exhaust ports 1a. Accordingly, outside air is sucked in from the air inlet 1b. The air, which has come in from the air inlet 1b via the filter unit 12, passes through the vent holes in the rotor core 7 and the gap between the outer peripheral surface of the rotor core 7 and the inner peripheral surface of the stator core 10. Then, the air comes to the ventilation fan 9 and is exhausted from the exhaust ports 1a by the rotation of the fan 9.
By passing the outside air through the motor body, as described above, the rotor bars 8, stator coil 11, bearings 4 and 5 and other parts of the motor are cooled. Thereby, the temperatures of the rotor bars 8, stator coil 11, bearings 4 and 5 and the grease for lubricating them are prevented from rising over the tolerable temperature range.
However, ambient air of the car-driving motor, which is mounted on the underfloor bogie of the car, contains a large quantity of dust that swirls while the car is running. Outside air to be sucked in the motor is not clean. To solve the problem, in the conventional car-driving motor shown in FIG. 1, dust in the outside air to be taken in the body of the motor is captured by the filter 12a of the filter unit 12 and the air is cleaned. With long-time driving of the motor, the filter 12a is gradually clogged and the amount of air passing through the motor body decreases. This poses a technical problem in that frequent periodical maintenance of the filter has to be conducted and a great deal of labor is needed for the maintenance.
To solve this problem, in recent years, a fully-opened-outer-fan-cooling type car-driving motor has been developed. A fully enclosed type motor with such an outer fan will now be described with reference to FIG. 2.
In FIG. 2, a bracket 14 is provided on a drive-side end portion of a bottomed cylindrical frame 13. A housing 3 is provided on a central part of a non-drive-side end portion of the frame 13. A stator core 10 is provided on an inner peripheral portion of the frame 13.
A rotor shaft 6 is rotatably supported on bearings 4 and 5 attached to the bracket 14 and housing 3. A rotor core 7 is fixed to an axially middle part of the rotor shaft 6. A drive-side end portion of the rotor shaft 6 is projected from the motor body, and a ventilation fan 15 is attached to the projected portion of the rotor shaft 6.
A number of axially extending cooling holes 16 are provided on the outer periphery of the frame 13. The cooling holes 16 define air passages 17. The air passages 17 are also formed in the bracket 14, and the drive-side of each air passage 17 is open toward the outer periphery of the ventilation fan 15. The non-drive-side of the air passages 17 is open to the outside. An air inlet 15a of the ventilation fan 15 on the drive-side of the motor defines an outside air intake port.
The fully enclosed type motor with outer fans, as shown in FIG. 2, is configured such that the inside of the motor is completely shielded from the outside. Thus, heat generated within the motor is mainly radiated via many cooling holes 16 provided on the outer periphery of the frame 13. In operation, the ventilation fan 15 is rotated to make outside air axially flow through the air passages 17 of the cooling holes 16 provided on the outer periphery of the frame 13. Thus, heat generated from the stator coil 11, which has conducted via the core 10 and frame 13, is radiated to the outside from the wall surface in the cooling holes 16.
In this fully enclosed type motor with outer fans, since outside air is not made to pass through the inside of the motor, the inside of the motor is not contaminated with dust. Further, since the outer part of the motor is cooled with outside air, there is an advantage that a filter for removing dust in outside air is needless.
There is known an example of the fully enclosed motor shown in FIG. 2, wherein a fan is provided outside the motor, and heat generated in the motor is forcibly radiated to the outside (e.g. Jpn. Pat. Appln. KOKAI Publication No. 57-77889).
However, in the fully enclosed motors shown in FIGS. 1 and 2, there are the following technical problems, and improvements in these car-driving motors have been desired.
First, the cooling performance of the rotor bars 8 is not good. Compared to the cooling of the stator coil 11 by means of heat transmission of the stator core 10, the rotor bars 8 are cooled by indirect heat transmission using air with low heat conductivity.
Consequently, heat of the rotor raises the temperature of the bearings 4 and 5 directly through the rotor shaft 6, or indirectly through heated air within the motor body. The tolerable temperature of the bearings 4 and 5 and the grease for lubricating them is lower than that of the rotor bars 8 and stator coil 11. The former is about haft the value of the latter.
In consideration of this fact, the motor has to be designed by taking into account the tolerable temperature of the bearings 4 and 5 and the grease, rather than the tolerable temperature of the rotor bars 8. As a result, the output power of the motor becomes lower than the conventional motors.
Moreover, since the temperature of the grease increases, the life thereof becomes shorter and the purpose of reducing the frequency of maintenance with use of the fully enclosed structure cannot be achieved.
Secondly, as shown in FIGS. 3 and 4 that depict a driving motor for a railway car, a vehicle that is called a bogie is mounted in chassis-related equipment. A driving motor 301 is secured by means of attachment arms 302 to an attachment seat 305 provided on a beam 304 of the bogie 303.
A coupler 306a is attached to a rotor shaft 306 of the driving motor 301 configured as shown in FIG. 1. The coupler 306a is, in turn, connected to a gear unit 307. The driving shaft of the gear unit 307 is a shaft 308 connected to the coupler 306a, and the driven shaft of the gear unit 307 is a wheel shaft 309. Wheels 310 are attached to both end portions of the wheel shaft 309. The wheels 310 can rotate and run on rails 311.
Bearings 312, which are mounted on the bogie 303, are attached to both end portions of the wheel shaft 309 and rotatably support the wheel shaft 309. A car body 313 is mounted on the bogie 303. If the motor 301 is powered on, a torque of the motor 301 is successively transmitted from the rotor shaft 306 to the coupler 306a to the gear unit 307 to the wheel shaft 309 to the wheels 310. Thus, the car body 313 is driven.
Design constraints peculiar to railway cars are imposed on the axial dimension L of the motor. That is, the axial dimension L is restricted by the inside width Ls between the wheels, as shown in FIG. 3, and cannot be made greater than the design requirement.
Thus, the motor has to be designed, while making the axial dimension of the motor as small as possible. To provide two fans that require large space is very disadvantageous.